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Lead-free dielectric ceramic capacitors are extensively studied for their environmental protection and excellent electrical properties. In this study, (1- x) Bi 0.47 Na 0.47 Ba 0.06 TiO 3 - x MgTiO 3 was synthesized by the classical solid-phase method. Perovskite materials usually have a complex structure, and the modification of the A-site and B-site doping can have a wonderful effect on the material. The effect of A-site Mg2+ doping on the phase structure and electrical properties of (1- x)BNBT- x MT was studied. Results showed that a wider optical band gap and a higher grain boundary density can be obtained by doping at the A-site, which greatly improved the breakdown electric field of the ceramics. X-ray diffraction, Raman scattering, transmission electron microscopy, and dielectric constant curves of (1- x)BNBT- x MT ceramics were also performed to characterize the transition between rhombohedral and tetragonal phases. The findings indicated that that doping at the A-site successfully induced the polar nanoregion, and the 0.94Bi 0.47 Na 0.47 Ba 0.06 TiO 3 -0.06MgTiO 3 relaxation ferroelectric ceramics had high W rec (5.82 J/cm3), stable frequency (W rec = 2.53 J/cm3±3 %, 1–200 Hz), excellent temperature stability (W rec ≈2.37 ± 3 % J/cm3, 30–100 °C), and fast discharge rate (4μs). This work can provide ideas for the development of green and harmless dielectric capacitors with high charge/discharge rate and high energy-storage density. [ABSTRACT FROM AUTHOR]